Information encoding apparatus and method, information decoding apparatus and method, recording medium utilizing spectral switching for embedding additional information in an audio signal

ABSTRACT

An information encoding apparatus and method, an information decoding apparatus and method, a recording medium, and a program make it possible to embed information without causing an increase in the amount of data of compressed audio signals. A spectrum measurer converts an audio signal from a time axis signal into a frequency axis signal. A compressor removes frequency spectra having levels below a minimum audible threshold value. An embedability determiner determines whether information can be embedded. A spectrum switcher embeds information in an audio signal by switching or by not switching predetermined first frequency spectrum and second frequency spectrum under the control of an information adder. The present invention is applicable to a disk recording apparatus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an information encoding apparatus andmethod, an information decoding apparatus and method, a recordingmedium, and a program and more particularly, to an information encodingapparatus and method, an information decoding apparatus and method, arecording medium, and a program that allow data to be embedded in audiosignals.

2. Description of the Related Art

Hitherto, as a method for compressing audio signals, there has beenknown a method in which frequency components not reaching a minimumaudible level curve are removed. The minimum audible level curve iscollective experimental values of the human-audible levels of pulsesounds having various different frequencies in a quiet environment. Thecurve is denoted as L in FIG. 1.

Referring to FIG. 1, the axis of abscissa indicates the frequencies ofthe spectra of audio signals, while the axis of ordinate indicates thelevels of the spectra of audio signals. The level of spectrum A isgreater than the value in the minimum audible level curve at thatfrequency, meaning that the level of spectrum A is above the minimumlevel audible to human ears, so that people can hear it. The level ofspectrum B is below the value in the minimum audible level curve at thatfrequency, meaning that the level of spectrum B is below the minimumlevel audible to human ears, so that people cannot hear it.

Conventionally, compression of audio signals has been accomplished byremoving the spectra whose levels are below the values in the minimumaudible level curve at particular frequencies (inaudible), as indicatedby spectrum B in FIG. 1. This compression method is used also in themoving picture experts group (MPEG) and other types of audio encodingmethods.

Conventional compression methods, however, have been disadvantageous inthat they cannot allow information to be embedded while compressingaudio signals at the same time. For example, it is possible to directlyembed information in a spectrum having a level below a value in theminimum audible level curve at the frequency. The embedded information,however, will add to the amount of information, because the spectrumhaving the embedded information cannot be cut off.

SUMMARY OF THE INVENTION

The present invention has been made with a view toward solving thetechnological problems described above, and it is an object of thepresent invention to allow audio signals to be compressed andinformation to be embedded at the same time.

An information encoding apparatus in accordance with the presentinvention includes a converting device for converting an input signalinto a spectrum signal, a removing device for removing the spectra offrequencies having levels below a minimum audible level curve amongspectra converted by the converting device, a first determining devicefor determining whether predetermined first frequency spectrum level andsecond frequency spectrum level are both above the minimum audible levelcurve, a second determining device for determining whether one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum level if the first and second frequency spectrumlevels are switched after the first determining device determines thatthe first frequency spectrum level and the second frequency spectrumlevel are both above the minimum audible level curve, an adding devicefor adding information by controlling to switch or not to switch thespectra on the basis of the information to be added if the seconddetermining device determines that one of the first frequency spectrumlevel and the second frequency spectrum level is below the minimumaudible level curve, when the first and second frequency spectrum levelshave been switched, and an encoding device for encoding a spectrum towhich information has been added by the adding device.

An information encoding method in accordance with the present inventionincludes a converting step for converting an input signal into aspectrum signal, a removing step for removing the spectra of frequencieshaving levels below a minimum audible level curve among spectraconverted by processing in the converting step, a first determining stepfor determining whether predetermined first frequency spectrum level andsecond frequency spectrum level are both above the minimum audible levelcurve, a second determining step for determining whether one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum level if the first and second frequency spectrumlevels have been switched after the processing of the first determiningstep determines that the first frequency spectrum level and the secondfrequency spectrum level are both above the minimum audible level curve,an adding step for adding information by controlling to switch or not toswitch the spectra on the basis of the information to be added if theprocessing of the second determining step determines that one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum audible level curve when the first and secondfrequency spectrum levels have been switched, and an encoding step forencoding a spectrum to which information has been added by theprocessing of the adding step.

A program recorded in a recording medium in accordance with the presentinvention includes a converting step for converting an input signal intoa spectrum signal, a removing step for removing the spectra offrequencies having levels below a minimum audible level curve amongspectra converted by the processing in the converting step, a firstdetermining step for determining whether predetermined first frequencyspectrum level and second frequency spectrum level are both above theminimum audible level curve, a second determining step for determiningwhether one of the first frequency spectrum level and the secondfrequency spectrum level is below the minimum level if the first andsecond frequency spectrum levels have been switched after the processingof the first determining step determines that the first frequencyspectrum level and the second frequency spectrum level are both abovethe minimum audible level curve, an adding step for adding informationby controlling to switch or not to switch the spectra on the basis ofthe information to be added if the processing of the second determiningstep determines that one of the first frequency spectrum level and thesecond frequency spectrum level is below the minimum audible level curvewhen the first and second frequency spectrum levels have been switched,and an encoding step for encoding a spectrum to which information hasbeen added by the processing of the adding step.

A program in accordance with the present invention includes a convertingstep for converting an input signal into a spectrum signal, a removingstep for removing the spectra of frequencies having levels below aminimum audible level curve among spectra converted by processing of theconverting step, a first determining step for determining whetherpredetermined first frequency spectrum level and second frequencyspectrum level are both above the minimum audible level curve, a seconddetermining step for determining whether one of the first frequencyspectrum level and the second frequency spectrum level is below theminimum level if the first and second frequency spectrum levels havebeen switched after the processing of the first determining stepdetermines that the first frequency spectrum level and the secondfrequency spectrum level are both above the minimum audible level curve,an adding step for adding information by controlling to switch or not toswitch the spectra on the basis of the information to be added if theprocessing of the second determining step determines that one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum audible level curve when the first and secondfrequency spectrum levels have been switched, and an encoding step forencoding a spectrum to which information has been added by theprocessing of the adding step.

An information decoding apparatus in accordance with the presentinvention includes a decoding device for decoding an input signal, afirst determining device for determining whether only one of a firstfrequency spectrum level and a second frequency spectrum level of asignal decoded by the decoding device is below a minimum audible levelcurve, a second determining device for determining whether only one ofthe first frequency spectrum level and the second frequency spectrumlevel is below the minimum level when the first and second frequencyspectrum levels are switched, and a reproducing device for reproducingadded information on the basis of determination results of the firstdetermining device and the second determining device.

An information decoding method in accordance with the present inventionincludes a decoding step for decoding an input signal, a firstdetermining step for determining whether only one of a first frequencyspectrum level and a second frequency spectrum level of a signal decodedby processing of the decoding step is below a minimum audible levelcurve, a second determining step for determining whether only one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum level when the first and second frequency spectrumlevels are switched, and a reproducing step for reproducing addedinformation on the basis of determination results obtained by theprocessing of the first determining step and the second determiningstep.

A program recorded in a recording medium in accordance with the presentinvention includes a decoding step for decoding an input signal, a firstdetermining step for determining whether only one of a first frequencyspectrum level and a second frequency spectrum level of a signal decodedby the processing of the decoding step is below a minimum audible levelcurve, a second determining step for determining whether only one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum level when the first and second frequency spectrumlevels are switched, and a reproducing step for reproducing addedinformation on the basis of determination results obtained by theprocessing of the first determining step and the second determiningstep.

A program in accordance with the present invention includes a decodingstep for decoding an input signal, a first determining step fordetermining whether only one of a first frequency spectrum level and asecond frequency spectrum level of a signal decoded by processing of thedecoding step is below a minimum audible level curve, a seconddetermining step for determining whether only one of the first frequencyspectrum level and the second frequency spectrum level is below theminimum level when the first and second frequency spectrum levels areswitched, and a reproducing step for reproducing added information onthe basis of determination results obtained by processing of the firstdetermining step and the second determining step.

In the information encoding apparatus and method, a recording medium anda program according to the present invention, when predetermined firstfrequency spectrum level and second frequency spectrum level are bothabove a minimum audible level curve, and the first frequency spectrumand the second frequency spectrum are switched, if one of the switchedspectrum levels is below the minimum audible level curve, theninformation is added by switching or not by switching the firstfrequency spectrum and the second frequency spectrum.

In the information decoding apparatus and method, the recording medium,and the program according to the present invention, information isreproduced on the basis of a result of the determination of whether afirst frequency spectrum level and a second frequency spectrum level areboth above a minimum audible level curve and a result of thedetermination of whether, when the first frequency spectrum and thesecond frequency spectrum are switched, one of the switched spectrumlevels is below the minimum audible level curve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a relationship between a minimum audible level curveand two frequency spectrum levels;

FIG. 2 is a block diagram showing a configuration example of aninformation processor to which the present invention has been applied;

FIG. 3 is a block diagram showing a configuration example of an encodershown in FIG. 2;

FIG. 4 is a flowchart illustrating the encoding processing carried outby the information processor shown in FIG. 2;

FIG. 5 illustrates a process of embedding data;

FIG. 6 illustrates another process of embedding data;

FIG. 7 illustrates yet another process of embedding data;

FIG. 8 illustrates still another process of embedding data;

FIG. 9 illustrates a further process of embedding data;

FIG. 10 is a block diagram showing a configuration example of aninformation processor to which the present invention has been applied;

FIG. 11 is a block diagram showing a configuration example of a decodershown in FIG. 10;

FIG. 12 is a flowchart illustrating the decoding processing carried outby the information processor shown in FIG. 10; and

FIG. 13 is a block diagram showing a configuration example of anembodiment of a computer to which the present invention has beenapplied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment in accordance with the present invention will now beexplained with reference to the accompanying drawings.

FIG. 2 shows an information processor to which the present invention hasbeen applied and which is adapted to embed information in an audiosignal. In an information processor 1 serving as an information encodingapparatus, an input audio signal is converted from an analog signal intoa digital signal by an A/D converter 11. The audio signal converted intothe digital signal is supplied to a spectrum measurer 12 so as to befurther converted into a spectrum signal by, for example, Fouriertransformation, for every predetermined unit time, and the spectrumlevel thereof is measured.

The audio signal whose spectrum level has been measured is supplied to acompressor 13 where it is compressed. In the compressing process,frequency spectrum B, the level of which is below a minimum audiblelevel curve L (FIG. 1) and therefore cannot be audibly recognized byhuman beings, is cut off. The compressed audio signal or spectrum signalis supplied to a spectrum switcher 14 for switching spectra.

The spectrum signal generated by the spectrum measurer 12 is alsosupplied to an embedability determiner 15 wherein it is determinedwhether information can be embedded by switching spectra. This will beexplained in more detail later in the description of the processing ofstep S14 shown in FIG. 4.

The result of the determination provided by the embedability determiner15 regarding whether the information can be embedded is sent to aninformation adder 16. If the embedability determiner 15 decides that theinformation can be embedded, then the information adder 16 supplies acontrol signal for controlling the switching of spectra to the spectrumswitcher 14 on the basis of the information to be embedded or added.

Based on the control signal from the information adder 16, the spectrumswitcher 14 switches spectrum signals supplied from the compressor 13.

An encoder 17 encodes spectrum signals supplied from the spectrumswitcher 14. The encoder 17 encodes audio data (the spectrum signals inthis case) by, for example, the adaptive dynamic range coding (ADRC).

FIG. 3 shows a configuration example of an encoder 17.

Audio data is input to a max/min value calculator 21. The max/min valuecalculator 21 calculates a maximum value and minimum value of the audiodata for each unit, and outputs the calculated minimum value MIN. Themaximum and minimum values are subtracted by a subtracter 22 to obtain adynamic range DR, which is output.

Furthermore, the difference between each level value and the minimumlevel value is calculated by a subtracter 24, the calculation resultsbeing sent to an adaptive quantizer 25. A delayer 23 holds off thetiming at which each level value is sent to the subtracter 24 by thetime required for the minimum level value to be sent to the subtracter24. If the number of quantization bits is n, then the adaptive quantizer25 divides the dynamic range DR by 2 n to determine the quantizationstep width, divides the subtraction result received from the subtracter24 by the quantization step width, and rounds off the division result toan integer so as to generate a quantization code Q. Thus, the encoder 7outputs the dynamic range DR, the minimum value MIN and the quantizationcode Q as compressed and encoded data.

The descriptions have been given of the example wherein the encoder 17uses the ADRC. Alternatively, however, the data may be processed usingother methods, including the discrete cosine transform (DCT) coding, thedifferential pulse code modulation (DPCM), vector quantization, sub-bandcoding and wavelet transform.

The data processed by the encoder 17 is supplied to a recorder 18 andrecorded in a recording medium, such as a disc (not shown). The data mayalternatively be sent out to a transmission line.

Referring now to the flowchart of FIG. 4, the coding procedure carriedby the information processor 1 shown in FIG. 2 will be explained.

In step S11, the A/D converter 11 converts a received audio signal froman analog signal into a digital signal.

In step S12, the spectrum measurer 12 transforms the audio signal on thetime axis, which has been converted into the digital signal, into aspectrum signal on the frequency axis by Fourier transformation or thelike. This processing is adapted to transform audio time signals intofrequency signals at predetermined time intervals.

In step S13, the compressor 13 compresses the audio signal by decimatingthe frequency spectra. More specifically, as described with reference toFIG. 1, the audio signal is compressed by decimating the frequencyspectra indicated by, for example, B in FIG. 1, whose level is below theminimum audible level curve and inaudible to human beings.

In step S14, the embedability determiner 15 determines whether data canbe embedded in the audio signal.

In this example, it is determined that the data can be embedded in theaudio signal if the following two conditions are met: Sa>C(fa) andSb>C(fb)Sa<C(fb) or Sb<C(fa) where the levels of two predeterminedfrequencies fa and fb are denoted as Sa and Sb and the functionimparting a minimum audible limit value for each frequency f is denotedas C(f), as shown in FIG. 5.

The first condition mentioned above means that both spectrum levels Saand Sb of the two predetermined frequencies fa and fb are above theminimum audible limit values corresponding to the frequencies. Hence,meeting the first condition means that the spectra of interest should betransmitted or should not be removed.

Satisfying the second condition means that, when the levels Sa and Sb ofthe two predetermined frequencies fa and fb are switched, one of theswitched levels is smaller than the minimum audible limit value.

For instance, the levels Sa and Sb of the spectra of the twopredetermined frequencies fa and fb shown in FIG. 5 are both above theminimum audible level curve L indicating the minimum audible limitvalues corresponding to the frequencies. When the spectrum positions ofthe two frequencies fa and fb shown in FIG. 5 are switched, the level Sbof the spectrum positioned at the frequency fa is larger than theminimum audible limit value, i.e., above the minimum audible level curveL, while the level Sa of the spectrum positioned at the frequency fb issmaller than the minimum audible limit value, i.e., below the minimumaudible level curve L, as shown in FIG. 6. Therefore, the spectra of thetwo frequencies fa and fb satisfies the second condition.

It is obvious that the second condition will be satisfied if the levelSa of the spectrum positioned at the frequency fb is larger than theminimum audible limit value and the level Sb of the spectrum positionedat the frequency fa is smaller than the minimum audible limit value whenthe positions of the levels Sa and Sb of the spectra of the twopredetermined frequencies fa and fb have been switched. Thisrelationship is established when the minimum audible limit value islarger at the frequency fa than at the frequency fb.

If, as shown in FIG. 7, the level Sa of the spectrum of the frequency faand the level Sb of the spectrum of the frequency fb are both smallerthan the minimum audible limit value, then the first condition will notbe satisfied. It is determined, therefore, that embedding is impossible.

Even if the level Sa of the spectrum of the frequency fa and the levelSb of the spectrum of the frequency fb are both larger than the minimumaudible limit value, satisfying the first condition, as shown in FIG. 8,it will be determined that embedding is impossible if both levels arelarger than the minimum audible limit value, failing to satisfy thesecond condition, as shown in FIG. 9, when the positions of the levelsare switched.

If it is determined in step S14 that data can be embedded in the audiosignal, then the information adder 16 determines in step S15 whether thedata to be embedded is 1.

The information adder 16 issues a control signal for switching thespectra if the logic of the data to be embedded in the audio data is 1,while it issues a control signal for not switching the spectra if thelogic is 0, i.e., it does not issue the control signal for switching thespectra.

As shown in FIG. 6, the spectrum switcher 14 switches, in step S16, thespectrum levels Sa and Sb of the two predetermined frequencies fa and fbof the spectrum signal supplied from the compressor 13 if the logic ofthe data to be embedded is 1, i.e., if the control signal for switchingspectra from the information adder 16 is received. In other words, thespectrum switcher 14 sets the spectrum level Sa at the frequency fa asthe spectrum level of the frequency fb, while it sets the spectrum levelSb of the frequency fb as the spectrum level of the frequency fa.

If the logic of the data to be embedded is 0, i.e., if the controlsignal for switching the spectra is not received from the informationadder 16, then the spectrum switcher 14 does not carry out theprocessing for switching the spectra, and maintains the original stateillustrated in FIG. 5, skipping the processing of step S16. The sameprocedure applies if it is determined in step S14 that the data cannotbe embedded.

Subsequently, in step S17, the encoder 17 encodes the spectrum signalsupplied from the spectrum switcher 14.

More specifically, the min/max value calculator 21 calculates themaximum and minimum values of a spectrum signal received for every unit.The subtracter 22 subtracts the minimum value from the maximum value tocalculate the dynamic range DR. The subtracter 24 subtracts a minimumvalue from the level of each spectrum signal whose timing has beenadjusted by the delayer 23, and outputs the result to the adaptivequantizer 25.

The adaptive quantizer 25 divides the dynamic range DR by 2 n tocalculate the quantization step width, divides the signal supplied fromthe subtracter 24 by the quantization step width, and rounds off thedivided value to an integer to compute the quantization code Q.

In step S18, the recorder 18 modulates the quantization code Q, theminimum value MIN and the dynamic range DR supplied from the encoder 17as record signals, and records them in a disc.

Thus, if an audio signal satisfies the data embedding conditions, 1-bitdata can be embedded as 0 if the levels Sa and Sb of the twopredetermined frequencies fa and fb are not switched, as illustrated inFIG. 5, or 1 if the levels Sa and Sb of the two predeterminedfrequencies fa and fb are switched, as illustrated in FIG. 6.

Regarding the frequency spectra within a unit time, the amount of datacan be increased to 2 bits the number of the combinations of the twopredetermined frequencies is set to 2 or 3 bits if the number is set to3. Furthermore, more data can be added by embedding data for a pluralityof units.

For instance, by using 8 bits for expressing one character, copyrightinformation, ID numbers, lyrics, artists' names and music categories canbe added to audio signals and recorded in discs or transmitted.

FIG. 10 shows a configuration of an information processor for decodingthe audio signals encoded as described above. In an informationprocessor 41, a reproducer 51 reproduces the signals recorded in a discand supplies the reproduced signals to a decoder 52. The decoder 52decodes the encoded audio signals. The decoded signals are supplied to aspectrum switcher 53 and an embedment detector 56.

The embedment detector 56 detects the presence of embedded data,generates a control signal for controlling the switching of spectra onthe basis of its detection result, and outputs the generated controlsignal to the spectrum switcher 53.

The spectrum switcher 53 switches the spectra on the basis of thecontrol signal from the embedment detector 56.

The embedment detector 56 also detects embedded bits and supplies themto an added information reproducer 57.

The added information reproducer 57 accumulates input bits and generatestext data based on the accumulated bits and outputs the generated textdata to a display unit 58 to display it.

A data decompressor 54 decompresses spectrum signals received from thespectrum switcher 53 by, for example, carrying out inverse Fouriertransformation or by converting frequency signals into time-axissignals, and outputs the decompressed signals to a D/A converter 55.

The D/A converter 55 converts the received signals from digital signalsinto analog signals and outputs the analog signals to a speaker or thelike (not shown).

The decoder 52 is constructed, for example, as shown in FIG. 11.

An adaptive inverse quantizer 71 divides the received dynamic range DRby 2 n to calculate a quantization step width, multiplies thequantization step width by a received quantization code Q, and outputsthe result to an adder 72. The adder 72 adds a received minimum valueMIN to the multiplication result supplied from the adaptive inversequantizer 71 so as to decode the data, and outputs the decoded data.

Referring now to the flowchart shown in FIG. 12, the decoding carriedout by the information processor shown in FIG. 10 will be explained.

In step S31, the reproducer 51 reproduces the signals recorded in adisc.

In step S32, the decoder 52 decodes the input audio signal. Morespecifically, the adaptive inverse quantizer 71 calculates aquantization step width by dividing the dynamic range DR by 2 n suppliedfrom the reproducer 51. The adaptive inverse quantizer 71 multiplies thequantization code Q received from the reproducer 51 by the calculatedquantization step width, and outputs the multiplication result to theadder 72. The adder 72 adds the multiplication result received from theadaptive inverse quantizer 71 to the minimum value MIN supplied from thereproducer 51 so as to decode the data.

In step S33, the embedment detector 56 determines whether data can beembedded in the audio signal. Whether data can be embedded is determinedin the same manner as that in step S14 shown in FIG. 4. Morespecifically, it is determined that the data can be embedded in theaudio signal if the following two conditions are met: Sa>C(fa) andSb>C(fb)Sa<C(fb) or Sb<C(fa) where the levels of two predeterminedfrequencies fa and fb are denoted as Sa and Sb and the functionimparting a minimum audible limit value for each frequency is denoted asC(f).

To be more specific, as shown in FIGS. 5 and 6, if only one of the twospectrum levels is smaller than the minimum audible limit value, i.e.,if the state is as shown in FIG. 6 (the spectra having been switched),or if only one level is smaller than the minimum audible limit value,i.e., if the state is as shown in FIG. 5 (the spectra having beenswitched), when the spectrum positions have been switched, then it isdetermined that data can be embedded. In any cases other than the above,it will be determined that data cannot be embedded.

If it is determined in step S33 that the audio signal can be embedded,then the embedment detector 56 determines in step S34 whether thespectra have been switched. If data can be embedded, then data is alwaysembedded in the frequency spectrum.

Referring to FIG. 6, the level Sa corresponding to the frequency fb issmaller than the minimum audible limit value. The spectra of the levelslower than the minimum audible limit value are basically removed, sothat they are not transmitted. Therefore, when the spectrum of the levellower than the minimum audible limit value is found, it may bedetermined that the audio signal has undergone the switching of thelevels Sa and Sb. This can be proved by the fact that, when thepositions of the spectrum levels Sa and Sb at the frequencies fa and fbhave been switched, the spectrum levels will both exceed the minimumaudible limit value.

Referring back to FIG. 5, if the spectrum levels Sa and Sb of the twofrequencies fa and fb of the received audio signal are both higher thanthe minimum audible limit values corresponding to the frequencies, thenit may be determined that the levels Sa and Sb of the two frequencies faand fb have not been switched.

If it is determined in step S34 that the spectra have not been switched,then the procedure proceeds to step S35 wherein the embedment detector56 determines that the embedded or added bit is 1 and outputs thedetermination result to the added information reproducer 57. Theembedment detector 56 also produces a control signal for switching thespectra and outputs the control signal to the spectrum switcher 53. Thespectrum switcher 53 switches the positions of the spectrum signalssupplied from the decoder 52 according to the control signal. Morespecifically, the spectrum switcher 53 sets the spectrum level Sa of thefrequency fa to the spectrum level of the frequency fb, while it setsthe spectrum level Sb of the frequency fb to the spectrum level of thefrequency fa.

If it is determined in step S34 that the spectra have not been switched,then the embedment detector 56 determines in step S37 that the embeddedor added bit is 0, and outputs the determination result to the addedinformation reproducer 57. In this case, the embedment detector 56 doesnot generate a control signal for switching spectra. In other word, theembedment detector 56 generates a control signal for not switchingspectra.

If it is determined in step S33 that data cannot be embedded, followingthe processing carried out in step S36 or step S37, the datadecompressor 54 carries out inverse Fourier transformation on the audiosignal, which has been converted by the compressor 13 from the time-axissignal to the frequency-axis signal, so as to converted it from thefrequency-axis signal back into the time-axis signal when encoding theaudio signal in step S38.

In step S39, the D/A converter 55 converts the audio signal from adigital signal into an analog signal and outputs the analog signal to aspeaker (not shown).

In step S40, the added information reproducer 57 accumulates the bitssupplied from the embedment detector 56, converts 8 bits intoone-character text data and outputs the text data to the display unit 58to display it. Thus, the information added to the audio signal isdisplayed. If the information is lyrics corresponding to the music ofaudio data, then a user can see the lyrics while reproducing the music.

If the information to be added is, for example, copyright informationprohibiting embedded audio signals from being copied, then it ispossible to prohibit the audio signals reproduced from a disc from beingrecorded in another recording medium on the basis of the copyrightinformation.

A series of steps of the processing described above can be implementedby hardware or software. To implement the processing by software, thesoftware is to be installed in a general computer or the like.

FIG. 13 shows a configuration example of a computer according to anembodiment to which a program for executing the aforesaid series ofprocessing steps has been installed.

A computer 91 includes a central processing unit (CPU) 101. Aninput/output interface 106 is connected to the CPU 101 via a bus 105.When the CPU 101 receives, via the input/output interface 106,instructions entered by a user who operates an input unit 108constructed of a keyboard, a mouse, etc., the CPU 101 runs the programstored in a read-only memory (ROM) 102.

Alternatively, the CPU 101 loads a program stored in a hard disk 104, aprogram transferred from a satellite or network, received by acommunication unit 109 and installed in the hard disk 104, or a programread from a removable recording medium 111 mounted on a drive 110 andinstalled in the hard disk 104, onto a random access memory (RAM) 103 toexecute the program.

Thus, the CPU 101 performs the processing according to the aforesaidflowcharts or the processing carried out in the configurationsillustrated by the block diagrams described above. The CPU 101 thenoutputs processing results through an output unit 107 constructed of aspeaker or the like, transmits them through a communication unit 109, orrecords them in the hard disk 104, as necessary, through theintermediary of, for example, the input/output interface 106.

The program can be recorded beforehand in the hard disk 104 or the ROM102 serving as a recording medium incorporated in the computer.

Alternatively, the program can be temporarily or permanently stored orrecorded in the removable recording medium 111, such as a Floppy(registered trade name) disk, a compact disc read-only memory (CD-ROM),a magneto-optical (MO) disc, a digital versatile disc (DVD), a magneticdisc, or a semiconductor memory. The removable recording medium 111 canbe provided as “package software.”

In addition to installing the program from the aforesaid removablerecording medium 111 into a computer, the program can be also wirelesslytransferred from a download site into a computer through theintermediary of an artificial satellite for digital satellite broadcastor wiredly transferred to a computer through a network, such as a localarea network (LAN) or the Internet. This allows the computer to receivethe program transferred as describe above through the communication unit109 and to install the program in the built-in hard disk 104.

In this specification, the processing steps constituting the program forcausing the computer to carry out various types of processing do notnecessarily have to follow the sequence indicated by the flowcharts intime series. The program also includes processing carried out inparallel or individually (e.g., parallel processing or object-orientedprocessing).

Furthermore, the program may be run on a single computer or a pluralityof computers in a distributed processing mode. Further alternatively,the program may be transferred to a remote computer wherein the programis executed.

1. An information encoding apparatus for encoding information andrecording the encoded information onto a computer-readable medium, theapparatus comprising: converting means for converting an input signalinto a spectrum signal; removing means for removing the spectra offrequencies having levels below a minimum audible level curve amongspectra converted by the converting means; first determining means fordetermining whether predetermined first frequency spectrum level andsecond frequency spectrum level are both above the minimum audible levelcurve; second determining means for determining whether one of the firstfrequency spectrum level and the second frequency spectrum level isbelow the minimum level if the first and second frequency spectrumlevels are switched after the first determining means determines thatthe first frequency spectrum level and the second frequency spectrumlevel are both above the minimum audible level curve; adding means foradding information by controlling to switch or not to switch the spectraon the basis of the information to be added if the second determiningmeans determines that one of the first frequency spectrum level and thesecond frequency spectrum level is below the minimum audible level curvewhen the first and second frequency spectrum levels have been switched;and encoding means for encoding a spectrum to which information has beenadded by the adding means.
 2. The information encoding apparatusaccording to claim 1, wherein the encoding means comprises: means fordetermining a minimum value and a maximum value of the input signal foreach predetermined unit; dynamic range calculating means for calculatinga dynamic range for each predetermined unit from the maximum value andthe minimum value for each predetermined unit; difference computingmeans for determining a difference between the input signal and theminimum value and outputting the determined difference; and a quantizingmeans for quantizing the determined difference on the basis of thecalculated dynamic range and outputting a quantized result.
 3. Aninformation encoding method for encoding information and recording theencoded information onto a computer-readable medium, comprising: aconverting step for converting an input signal into a spectrum signal; aremoving step for removing the spectra of frequencies having levelsbelow a minimum audible level curve among spectra converted byprocessing in the converting step; a first determining step fordetermining whether predetermined first frequency spectrum level andsecond frequency spectrum level are both above the minimum audible levelcurve; a second determining step for determining whether one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum level if the first and second frequency spectrumlevels have been switched after the processing of the first determiningstep determines that the first frequency spectrum level and the secondfrequency spectrum level are both above the minimum audible level curve;an adding step for adding information by controlling to switch or not toswitch the spectra on the basis of the information to be added if theprocessing of the second determining step determines that one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum audible level curve when the first and secondfrequency spectrum levels have been switched; and an encoding step forencoding a spectrum to which information has been added by theprocessing of the adding step.
 4. A computer-readable recording mediumstoring a program that when executed by a computer for controlling aninformation encoding apparatus performs a method comprising: aconverting step for converting an input signal into a spectrum signal; aremoving step for removing the spectra of frequencies having levelsbelow a minimum audible level curve among spectra converted by theprocessing in the converting step; a first determining step fordetermining whether predetermined first frequency spectrum level andsecond frequency spectrum level are both above the minimum audible levelcurve; a second determining step for determining whether one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum level if the first and second frequency spectrumlevels have been switched after the processing of the first determiningstep determines that the first frequency spectrum level and the secondfrequency spectrum level are both above the minimum audible level curve;an adding step for adding information by controlling to switch or not toswitch the spectra on the basis of the information to be added if theprocessing of the second determining step determines that one of thefirst frequency spectrum level and the second frequency spectrum levelis below the minimum audible level curve when the first and secondfrequency spectrum levels have been switched; an encoding step forencoding a spectrum to which information has been added by theprocessing of the adding step; and an output step for outputting theencoded spectrum.
 5. An information decoding apparatus comprising:decoding means for decoding an input signal; first determining means fordetermining whether only one of a first frequency spectrum level and asecond frequency spectrum level of a signal decoded by the decodingmeans is below a minimum audible level curve; second determining meansfor determining whether the first frequency spectrum level and thesecond frequency spectrum level are both above the minimum level whenthe first and second frequency spectrum levels are switched; reproducingmeans for reproducing added information on the basis of determinationresults of the first determining means and the second determining means;and outputting the information.
 6. The information decoding apparatusaccording to claim 5, wherein the input signal is a signal obtained byquantizing a minimum value of a signal for every predetermined unit, adynamic range of the signal for the every predetermined unit and adifference between the signal and the minimum value for the everypredetermined unit on the basis of the dynamic range, and the decodingmeans comprises: inverse quantizing means for calculating a quantizingstep width from the dynamic range, inversely quantizing the quantizedsignal and outputting the inversely quantized signal; and adding meansfor adding the minimum value to the inversely quantized signal.
 7. Aninformation decoding method comprising: a decoding step for decoding aninput signal; a first determining step for determining whether only oneof a first frequency spectrum level and a second frequency spectrumlevel of a signal decoded by the processing of the decoding step isbelow a minimum audible level curve; a second determining step fordetermining whether the first frequency spectrum level and the secondfrequency spectrum level are both above the minimum level when the firstand second frequency spectrum levels are switched; a reproducing stepfor reproducing added information on the basis of determination resultsobtained by the processing of the first determining step and the seconddetermining step; and an outputting step for outputting the information.8. A computer-readable recording medium storing a program that whenexecuted by a computer controls an information decoding apparatus toperform a method comprising: a decoding step for decoding an inputsignal; a first determining step for determining whether only one of afirst frequency spectrum level and a second frequency spectrum level ofa signal decoded by processing of the decoding step is below a minimumaudible level curve; a second determining step for determining whetherthe first frequency spectrum level and the second frequency spectrumlevel are both above the minimum level when the first and secondfrequency spectrum levels are switched; a reproducing step forreproducing added information on the basis of determination resultsobtained by the processing of the first determining step and the seconddetermining step; and an output step that outputs the added information.